Condensation flow patterns inside plain and microfin tubes: A review

Nowadays, plain and microfin tubes are largely used in refrigeration and air conditioning industries for condensation inside macroscale tubes. The mechanisms of condensation heat transfer and pressure drop are tightly linked with the prevailing two-phase flow regime, but not much evidence about the effect of microfins on the condensation flow patterns is still available in the open literature. A deep overview about the relevant literature on two phase flow pattern visualization inside tube considering experimental techniques, suggested flow regime maps and models for heat transfer coefficient is presented. Furthermore, this paper presents the extensive experimental contribution of the Authors with smooth and microfin tubes. The collected data for plain tube are compared against different flow pattern maps. The flow visualizations obtained for microfin tube are compared with those of plain tube; moreover, two flow regime maps proposed by present Authors for smooth and enhanced tubes are validated.